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Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 2002
SMALL COMMERCIAL FISHING VESSEL STABILITY ANALYSIS
WHERE ARE WE NOW? WHERE ARE WE GOING?
John Womack, St. Michaels Ship Design
34600 Warren Road, Pittsville MD 21850
shipsjw@aol.com
SUMMARY
Small commercial fishing vessels are the largest, most diverse, and constantly evolving class of marine vessels in existence. Yet the methods used to evaluate their stability are a one size fits all with little improvement over the many decades since their introduction in the early 1900's. This conflict coupled with significant flaws in the methods used to convey stability guidance to the crews leads to unacceptable risks being taken and fishing vessels and their crews being lost. Improvements are needed in all areas of small commercial fishing vessel analysis;better criteria that reflect the true dynamic environment faced by the crews, better means toconveystability guidance including the current risk of capsize to the crews, and lastly a program to teach stability and how to use the guidance provided.
1. INTRODUCTION
Small commercial fishing vessels, generally less than 150 feet (50 meters) in length, are the most diverse and largest class of marine vessels in existence. There are few common characteristics in hull shape, general arrangements including deckhouses, and fishing methods among the many fisheries worldwide. Even within a particular fishery, many differences in the vessels may exist.
Yet, the stability evaluation methods available today are mostly of a generic one size fits all boats, all seas, and all fishing methods. And the basis for the most common of the standards, the area under the righting arm curve to various angles of heel, is from work done in 1939 for North European coastal traders with little updating in the intervening years. Lastly, if the vessel is less than 79 feet (24 meters), there are no universally accepted stability evaluation methods available.
In part because of this conundrum, the commercial fishing industry is the one of the most dangerous, and deadly, occupations in many countries. Fishers in the United States in 2000 ranked second in deaths per 100,000 workers, right behind timber cutters and well above airline pilots, police, and construction workers. Further, in recent studies by Stephen Roberts of the University of Oxford
(Roberts 2002) showed fishers had the most dangerous job in Britain. They were 50 times more likely to have a fatal accident over the last twenty years than the average worker.
Clearly, improving the stability evaluation methods is warranted to further the safety in the commercial fishing industry. But this is only part of the solution required; additional improvements in how a "stability analysis" is performed on a fishing vessel must be done.
This paper will explore the practical issues faced by today's naval architects in doing a satisfactory stability analysis on small commercial fishing boats. First, what are all of the parts required for a satisfactory stability analysis; the stability evaluation methods, the presentation of the stability guidance, and the education of the crews in stability concepts? And secondly, how can those parts be accomplished in a practical fashion; the strengths and weakness of the currently available means and the need for future development?
2. DEFINING WHAT IS A SMALL COMMERCIAL
FISHING VESSEL STABILITY ANALYSIS
What is a small commercial fishing vessel stability analysis? It is not just the mathematical calculations done by Naval Architects. A correct stability analysis must also include the presentation of the stability guidance developed to the crews and the teaching of how to correctly use that guidance. This requirement for an integrated process from the technical creators to the end users is the only way to ensure the final goal, the safety of the crews.
Logically, this makes common sense. The best evaluation of a fishing boat's stability by the naval architect is of no value if the resulting stability guidance is not clearly communicated to the crews who must use it. And the best stability guidance is of no value if the crews are not taught how to use it or simply believe it is not correct.
Unfortunately, parts of this process are often lost in the many conflicts occurring in today's fisheries. Cost is always a concern, especially with many fisheries under economic pressure. And the cost comes in two varieties; direct dollars from the additional work done by the naval architect as well as the time spent by the crew not catching fish. And there is always the underlying mistrust between the crews and the naval architects over who best knows how to operate the vessel; those who go to sea or those who have the technical skills (the answer is both).
The end results of better stability guidance are well worth overcoming these conflicts. The additional direct cost increases will be minimal once standard evaluation methods and stability guidance procedures have been developed. And with a comprehensive training program to teach stability to the crews, the underlying mistrusts can be resolved.
3. PROVIDING STABILITY GUIDANCE TO
FISHING BOAT CREWS
Currently, the primary means for providing stability operating guidance to small fishing boat crews is the "Stability Letter". These stability letters are generally a simplified version of the traditional "Stability Book" that is generated for large commercial boats. These simplified stability letters have been the preferred means of conveying the critical stability information and boat operating guidance to crews given the simpler configuration of small fishing boats and the lower or non- existent training levels for many of the crews.
For a stability letter to be effective, it must first be understandable to the crews, and second, the crews must believe that the guidance information provided is correct. While the first requirement is fairly obvious, the second requirement is equally important. The best stability letter on the most seaworthy boat in the world is of no value if the crew believes the loading requirements are wrong and ignores the stability guidance. Unfortunately, most forms of the stability letters currently in use are neither readily comprehensible and/or are trusted by the crews (Johnson and Womack 2001).
3.1 KEY AREAS TO IMPROVE STABILITY
GUIDANCE
The problems that exist with current types of stability letters used to provide stability to small fishing vessel crews are the principal reason crews are disregarding these letters, either intentionally or because the guidance is incomprehensible, and putting themselves in danger. Fishing boat crews don't have a death wish; they just truly don't understand the potential adverse impacts on their boat's overall stability when they load the boat to make it "feel" better under normal fishing operations (Johnson and Womack 2001).
Since the principal blame for the problems with stability letters lies with the naval architects and marine surveyors who create them, it is they who must find the solutions. But they must understand what the fishermen need and how fishing works in developing the fixes. The solutions for improving stability guidance to small commercial fishing vessel crews are simple.
1. Be written to provide stability guidance, not to dictate the boat's operation.
2. Present the safe loading conditions clearly, both visually and written.
3. Provide some means for conveying the stability levels, i.e. risk of capsizing, associated with each of the loading conditions.
4. Be comprehensible by crews with little or no formal training.
5. Use practical operating restrictions on variable catch limits, etc.
6. Use practical means to allow the crew to check if the boat is loaded correctly.
7. Develop a series of operating guidelines on proper seamanship and boat maintenance suitable for insuring a boat's adequate stability.
In summary, the goal is to provide the captain with practical stability guidance and a way to gauge the risks of capsizing based on loading, weather, and other factors, and let them run their boats.
3.2 PROVIDING RISK BASED STABILITY
GUIDANCE BY LOAD MATRIXES
Loading matrixes (see Figure 2 for an example, additional examples to be shown during the Workshop) have been proposed (Johnson and Womack 2001) to meet the goals presented above. The matrixes are easy to use while showing all potential loading conditions on a single page.
With catch levels on the left column and various tank and deck loadings across the top and bottom, it is easy for the crew to check if their boat's stability is acceptable.
Figure 2: Sample Safe/Unsafe Loading Matrix
These risk based loading matrixes, particularly the color versions, offer many advantages to the crews in safely operating their vessel. First the color gives very quick intuitive indications of the current risk of capsize for any conceivable loading condition. Second, the matrixes allow the crew to plan ahead to ensure adequate stability. With all of the loading conditions on single sheet, the crew can literally plot their trip on the load matrix and adjust loading, ballast, or fuel levels to suit.
This type of loading matrix also has the advantage of putting the operational decisions for the boat back to the captain instead of with the naval architect as current safe/unsafe stability letters do. This approach does require that the captain, vessel owner, and other decision makers must clearly understand the basic concepts of stability in order to select the appropriate risk level, given current and predicted weather conditions and other trip factors.
4. STABILITY GUIDANCE EDUCATION FOR
FISHING BOAT CREWS
Assuming the stability letter adequately provides the necessary stability operating guidance, the crews must also believe that the guidance provided is correct so they will follow it. Unfortunately, from many casualties reports in the United States and first hand experience, the crews often ignore stability letters because they believe they, not the Naval Architects, know how to load the boat correctly. (Johnson & Womack 2001, USCG 1999)
The solution is simple; improve the training of basic stability concepts to fishing boat crews so they can better understand and trust their letters. From discussions with fishing boat crews, they are interested in understanding their stability letters. The problem is the creation of the stability letter appears to be a lot of black magic by the naval architect. From moving some weights back and forth on their boat, the architect comes back with a piece of paper on how to load their boat. And often, the stability instructions may run counter to how they believe their boat should be loaded or restricts the maximum allowable catch to levels below what they are carrying now.
To teach stability to fishing boat crews will require explaining fishing boat stability and its complex interactions to crews who generally lack a higher education. Common naval architecture terms used in stability are simply unknown, and often incomprehensible, to the crews. For example, even the basic concept of center of buoyancy, intuitively understood by naval architects, is unknown to many crews. The challenge will be in convincing the crew that the center of buoyancy is a real location that all of the buoyant forces are acting through, not an imaginary point on their boat that the crews may have a hard time conceiving.
The course needs to only teach the basic concepts of stability and the effect of typical fishing operations on a boat's stability. The course should not teach how stability is calculated, that is the responsibility of the naval architect who thoroughly understands all of the nuances of stability.
The primary goals for the proposed stability training
course are:
1. Explain what the center of gravity (G) and center
of buoyancy (B) are.
2. Show how the relationship between G and B
works to keep the vessel upright as it heels.
3. Explain the basic methods of determining if a
vessel has adequate stability.
4. Show the effect on a vessel's stability from typical
fishing operations.
The basic layout of the stability training course consists of two parts; a written manual and a verbal presentation. The two individual components of the training course will be developed to be mutually supporting. Figures in the written manual would be similar to the displays and models used in the presentation, and concepts demonstrated in the presentation would be in the manual. This will allow crews that have taken the training course to use the written manual as follow-up take-home notes to the verbal presentation.
Figure 3: Example Training Manual Figure
Figure 4: Example Training Manual Figure
The written manual will be developed to be self- explanatory to persons who have some formal education or seamanship training. The figures intended to show the basic stability concepts would be kept simple and structured to appear similar to existing fishing boats designs. It is important to make the figures believable to the crews. If they look similar to their boat, the chances are better the crew will believe the message even when it runs counter to past beliefs. Figure 3 to 5 are examples of the proposed figures (more will be shown during the Workshop).
Figure 5: Example Training Manual Figure
The second component of the training course, the verbal presentation, will be developed for both small and large groups. The small group is intended to be an individual fishing boat's crew and owner, with the larger groups being at meetings such as trade shows or National Marine Fisheries Service regional council meetings. The
presentation for individual boats will be made easily
transportable to allow the presentation to be made onboard,
at dockside, or even in the local watering hole. This will
allow a naval architect to give the presentation when
delivering a stability letter to a boat.
For both presentation sizes, visual displays and static and dynamic demonstration models would be used. The visual displays would be enlarged versions of the training manual figures, posters, slides or computer driven graphics. The models are an important part of the presentation as they allow the crews to see "hands-on" what is happening during typical fishing operations. As an example, the
crews can see directly the loss of stability when they boat is overloaded or the negative effects of slack tanks. Actually "capsizing" the model, especially when they believe they have loaded the model to make it safer, is a very convincing training method. (Johnson & Womack 2001)
From practical experience it is important that with presentations for individual vessels, actual graphs of that vessel's righting arms be integrated into the presentation figures. Stability strengths or weakness particular to the subject vessel can be clearly shown.
6. CONCLUSION
By improving all three areas required for providing stability guidance to small commercial fishing vessels; stability criteria, stability letters, and education, we can significantly improve the safety of the crews. New stability criteria need to be developed to reflect today's fishing vessels and the sea conditions they operate in. New means to convey the stability guidance to the crews also need to be developed, particularly the current risk of capsize. And lastly to tie this all together, an integrated program to teach the basic concepts of stability and the crew's effect on stability needs to be developed.
7. REFERENCES
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Johnson, B., and Womack, J. 2001, On Developing a Rational and User-friendly Approach to Fishing Vessel Stability and Operational Guidance, Proceedings of the 5th International Ship Stability Workshop, Trieste Italy, Sept 2001.
Johnson, B., and Grochowalski, S., 2002. Development of a Performance Based Fishing Vessel Stability Criteria, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002.
Rahola, J., 1939. The Judging of the Stability of Ships and the Determination of the Minimum Amount of Stability. Doctoral Thesis, The University of Finland, May 1939.
Roberts, S. E., 2002. Hazardous Occupations in Great Britain, Lancet 2002; 360: 543-44.
Spyrou, K. J., 2002. A Basis for Developing a Rational Alternative to the Weather Criterion: Problems and Capabilities, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002.
Umeda, N., and Peters, A., 2002. Recent Research Progress on Intact Stability in Following/Qartering Seas, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002.
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USCG 1999. Dying to Fish: Fishing Vessel Casualty Task Force Report, USCG, March 1999. |
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